The invention relates to weft insertion apparatus for shuttle-type weaving looms, and more particularly to apparatus of this general kind having facilities for periodically actuating a piston rod coupled to a gripper shuttle with a pressurized fluid to initiate a launch stroke of the shuttle.
A particularly advantageous hydraulically-instrumented arrangement of this type has been proposed in the copending, coassigned application Ser. No. 718,793, filed Aug. 30, 1976 and entitled "TECHNIQUE FOR CONTROLLABLY RECIPROCATING THE WEFT INSERTION PORTION OF A SHUTTLE-TYPE WEAVING LOOM". In such arrangement, hydraulic fluid is cyclically transferred from a first main fluid reservoir to points at the rear and forward end, respectively, of the piston rod. A second elastomeric fluid reservoir is disposed behind a perforated rear wall of a cylinder that supports the piston rod during its movement for storing fluid transferred to the rear end of the piston in preparation for the next-occurring launch stroke. In order to initiate the launch stroke, fluid is first abruptly released from the front of the piston, and thereafter fluid is introduced into the elastomeric reservoir to propel the piston rod, and thereby the gripper shuttle, forwardly into its operated position. With this expedient, the forward stroke of the piston rod proceeds without resistance caused by hydraulic pressure in front of the piston rod.
To initiate the return stroke, fluid is re-introduced from the first reservoir to the front end of the piston, and during the return stroke the fluid in the elastomeric reservoir behind the piston rod is simultaneously withdrawn into the first reservoir so that the return stroke proceeds without having to overcome the resistance of hydraulic pressure at the rear of the piston.
The fluid pressure at the front end of the piston rod is thereafter maintained until after a re-charging of the elastomeric reservoir, thereby preventing inadvertent release of the piston rod prior to its designated time of actuation for the next launch stroke.